Bio-based L-lysine phosphate/dicyandiamide/silica sol composite system for highly efficient green flame retardancy of cotton fabrics
Yuli Zhang, You Fei, Hao Huang, Zhenhua Wang, D. Liu
Abstract
To address the flammability of cotton fabrics, an innovative flame-retardant system based on synergistic action between amino acid-derived bio-based flame retardants and silica sol has been developed. Using L-lysine and urea as nitrogen sources, and phosphoric acid as an acid source, a biomass flame retardant—the L-lysine-phosphoric acid-urea complex (LPU)—was successfully synthesized. This complex was then combined with dicyandiamide (DCD) to form the LPU/DCD solution. Through impregnation-drying, SiO<sub>2</sub> sol and LPU/DCD solution were sequentially applied to the cotton fabric surface, constructing an integrated coating of phosphorus, nitrogen, and silicon elements. The composite flame-retardant solution was coated onto the cotton fabric surface using the impregnation-drying method. Functional groups, surface chemical composition, matrix crystal structure, microstructure, surface elemental composition, and distribution were characterized for both untreated and treated cotton fabrics using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX). Results indicate that SiO<sub>2</sub>-LPU/DCD@COT exhibits optimal flame retardancy, with a significantly increased initial pyrolysis temperature and a residual carbon content as high as 53.37%. Its limiting oxygen index (34.3%) improved by 86.41% compared to the original cotton fabric (18.4%), achieving a non-combustible level. Its pHRR (32.04 kW/m<sup>2</sup>), THR (4.95 MJ/m<sup>2</sup>), and FIGRA (0.45 kW/m<sup>2</sup>·s) decreased by 86.80%, 49.07%, and 94.07%, respectively, compared to the original cotton fabric. with the highest SE value reaching 1.42 (≥ 1.0), indicating excellent synergistic flame retardancy between SiO<sub>2</sub> and LPU-DCD. This study provides a novel strategy for preparing bio-based flame-retardant cotton fabrics.